1. Field of the Invention
The present invention relates generally to a system for treating ballast water used in a ship and a method of controlling the system and, more particularly, to a ballast water treatment system having a back-pressure formation unit and a control method thereof, in which control method back-pressure in a filtering unit is checked and formed during a back washing operation for a filter of a filtering unit, thus enabling the back washing operation to be efficiently performed. Both a method of physically filtering ballast water using the filter of the filtering unit and a method of sterilizing ballast water using ultraviolet rays are used to treat ballast water, thus preventing secondary contamination due to byproducts, preventing the contamination of a ballast tank. The flow rate of ballast water introduced into an ultraviolet treatment unit is controlled such that the efficiency of the ultraviolet treatment unit is not reduced, while back-pressure is formed in the filtering unit, thus increasing the overall treatment efficiency of the ballast water treatment system. The filtering unit or the ultraviolet treatment unit may be automatically washed, thus always maintaining uniform performance and enabling efficient maintenance.
2. Description of the Related Art
Ballast water is the seawater that is put into a ballast tank of a ship in order for the ship to maintain its balance while sailing without goods. The increasing volume of internal trade has led to an increase in the ratio of marine transportation, so that the numbers and size of the ships have also been rapidly increasing. Thus, the volume of ballast water used in ships has also increased considerably. As the volume of the ballast water used in the ship has increased, damage done to the endemic marine ecosystem resulting from it being attacked by exotic marine organism species is also increasing. In order to address the international environmental contamination problem, the Internal Maritime Organization (IMO) completed the ‘International treaty concerning control and management of ballast water and sediment of ships’ in 2004, which became effective in 2009.
The ballast water contains various kinds of microorganisms, thus causing marine contamination and disturbing the ecosystem. Thus, these microorganisms and inorganic sources of contamination must be treated. Conventional methods of treating ballast water include a marine treatment method of exchanging ballast water in the sea and a land treatment method but they are ineffective. Thus, a method of installing a ballast water treatment system in a ship has been widely used. The ballast water treatment system mainly uses filtering, heat treatment, chemical treatment, electrolysis, ozone treatment or ultraviolet ray radiation, etc.
However, the heat treatment is problematic in that it is difficult to treat microorganisms or inorganic sources of contamination which are resistant to heat. The chemical treatment is problematic in that secondary contamination may occur after ballast water has been treated. Further, the electrolysis or ozone treatment is problematic in that an explosion may be caused by a short circuit and it is inefficient to manage. The filtering is problematic in that sediment must be removed from a filter. Further, the ultraviolet ray radiation is problematic in that its efficiency is low because of foreign substances adhering to the surface of a sleeve which surrounds an ultraviolet lamp.
FIG. 1 is a schematic view showing a conventional filtering-type ballast water treatment system. In the conventional filtering method, when a washing operation of removing foreign substances from an inner surface of a filter a1 in a filtering unit a is performed, internal pressure of the filtering unit a must be higher than external pressure of the filtering unit a (i.e., internal pressure of a washing unit a2 sucking foreign substances from the inner surface of the filter a1). That is, in order to perform a smooth washing operation, back-pressure must be formed. The term ‘back-pressure’ used herein means pressure which is set such that internal pressure of a body a3 of the filtering unit a is larger than internal pressure of the washing unit a2 sucking the foreign substances from the inner surface of the filter a1, thus allowing the ballast water and the foreign substances to move from the body a3 of the filtering unit a to the washing unit a2. If a ballast tank b for storing filtered ballast water is empty or the amount of the ballast water stored in the ballast tank b is small even though the filtering unit a is pressurized using a ballast water pump to supply ballast water, a required back-pressure is not formed, so that a smooth washing operation is impossible. Especially, as shown in FIG. 2, because of a spatial restriction of a space in which the ballast water treatment system is installed, for example, a ship, the filtering unit a may be located at a position higher than that of the ballast tank b. In this case, the loss of water head occurs, so that it is more difficult to maintain the back-pressure. In spite of the restriction, there is a demand for a system for allowing foreign substances in the filter to be smoothly washed.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a ballast water treatment system having a back-pressure formation unit and a control method thereof, in which back-pressure in a filtering unit is checked and formed during a back washing operation for a filter of the filtering unit, thus enabling the back washing operation to be efficiently performed.
Another object of the present invention is to provide a ballast water treatment system having a back-pressure formation unit and a control method thereof, in which both a method of physically filtering ballast water using a filter and a method of sterilizing ballast water using ultraviolet rays are used to treat ballast water, thus preventing secondary contamination due to byproducts, preventing the contamination of a ballast tank, enabling efficient maintenance, and making the system easy to control.
A further object of the present invention is to provide a ballast water treatment system having a back-pressure formation unit and a control method thereof, in which a flow rate of ballast water introduced into an ultraviolet treatment unit is controlled such that the efficiency of the ultraviolet treatment unit is not reduced, while back-pressure is formed in a filtering unit, thus increasing the overall treatment efficiency of a ballast water treatment system.
Yet another object of the present invention is to provide a ballast water treatment system having a back-pressure formation unit and a control method thereof, in which a filtering unit or an ultraviolet treatment unit may be automatically washed, thus always maintaining uniform performance, and enabling efficient maintenance.
A still further object of the present invention is to provide a ballast water treatment system having a back-pressure formation unit and a control method thereof, in which a bypass duct may be further provided between a filtering unit and an ultraviolet treatment unit, thus allowing ballast water to be treated while passing through only either the filtering unit or the ultraviolet treatment unit, as necessary.